Thursday, February 4, 2021

Rockslide and unstable slope to keep US 2 Pine Canyon closed

Update: March 5, 2021
The weather has been favorable and our contractor has made great progress removing the unstable rock from the hillside, including the car-sized boulder that was hanging above the roadway. The work is accomplished by manually wedging off this material. Technicians that complete this work wear safety harnesses secured above the slope, and it must be done skillfully.

After the unstable material was removed this past week, the contractor brought in a 144-foot crane used to install rock dowels that will secure unstable rock on the face of the cut. They are also repairing and extending the slope netting that was damaged during the slide. When the rock doweling is complete and new anchors are secured, the netting can be rehung and extended. The repaired and improved slope netting will now cover a total of 4,500 square feet more rock slope at this location in Pine Canyon.

When will the road reopen?
The work currently requires the crane to be staged in the middle of the roadway. Situating the crane takes time to set up and regularly reopening for traffic to move through the work zone would not allow for the contractor to complete the work in a safe and timely manner. Once the crane no longer needs to be in the roadway and it does not compromise safety, we will reopen the road with flagger-controlled traffic during the work day. We expect the project to wrap up by March 24.

Update: Feb. 18, 2021
Recent winter storms have covered the US 2 Pine Canyon slope in a layer of snow, which created safety concerns as the contractor can't determine where the cracks are located on the slope. Work is on hold as we wait for the snow to melt off but warmer weather and rain is in the forecast starting Monday, Feb. 22 so it appears the contractor can get back out there to scale off the boulder, repair netting and clear debris.

While the weather delay has cost a few days work, our contractor is experienced and expects to wrap up work the last week of March, assuming conditions remain safe. Reminder that the highway is closed until that time.

Emergency work could keep highway closed into March

By Lauren Loebsack

We've seen a lot of debris slides so far this year in the wake of heavy precipitation, and the most recent one came early Tuesday morning, Feb. 2, when the upper section of a rock slope above US 2 about four miles east of Orondo in Douglas County fell, covering most of the roadway at milepost 143.7. The slide pulled the cable netting into the slide area and sheared off one of the cable anchors that attach the netting to the hillside.
A drone's-eye-view of the slide shows where the netting was pulled into the slide area and the newly
exposed boulder above the netting at the crest of the slope.

The rockslide dropped about 300 yards of debris including very large rocks, leaving the highway closed. Just as concerning, it left a boulder the size of a truck that is now hanging out above the highway. There is a tension crack behind the boulder that indicates it is at risk of falling and must be removed manually. The netting will also need to be extended and re-secured to the slope before the debris on the highway can be cleared. This will require a contractor that specializes in this type of work.
A close-up look at the cable net anchor that has been sheared

Fortunately, no one was hurt but the road will remain closed for some time. How long? Hard to say. We're moving forward with an emergency contract to get started as soon as possible but we estimate it could take about six weeks, reopening sometime in March. Until the road is reopened, please avoid the area. Never go around road closed signs as they are there for everyone's safety.

But I thought there was a net?
When we install netting and anchors on a hillside, they are designed both to stop smaller rocks from bouncing onto the highway and to stop catastrophic failures of a slope. IAn this case, it did. The slide could've been much worse. But this slope is undergoing a natural process called calving. You may have seen this happen on TV shows about glaciers when ice shears off and breaks away. Same thing with hillsides. Essentially rocks are breaking away from the hillside. The netting does all it can to prevent massive amounts of the slope to come down, but there's only so much they are designed to handle.
The newly-exposed rock at the crest of the slope (red dashed). Note that the east end of the cable net has been pulled from its original location (red arrows). Also note the newly exposed rock block at the top of the slope (yellow dashed).

OK, so what's next?
We know this closure is challenging for people who regularly travel through this area. There are really no great ways around the closure and there is no set detour. We encourage people to consult local maps to determine the best route to get where you're going.
About 300 yards of rock has fallen across both lanes of US 2

Once a contractor has been secured, we'll have a clearer picture of the timeline. We'll update this blog when we know more. You can also follow us on Twitter or sign up for our email/text alerts for updates.
The newly exposed rock must be removed from the slope prior to resecuring and extending the netting (yellow dashed).


Unknown said...

Blast everything on that slope and it won't. Be a problem anymore.shouldnt take 6weeks either.

Stephanie said...

It is unfortunate to see that this has happened, but it is great news that no one was hurt. Thank you for sharing the close up photos of the failure and the steps you're taking to repair the damage.

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